Question

I’m very new to Ruby..consider the code below I kind repeat the if else statement in every sub class. Is there a way to group this into superclass’s initializer? Thanks for any help!

class TreeItem
    def TreeItem.new(*args)
        if self== TreeItem
            raise "Attempt to create TreeItem"
        else
            super
        end
    end

    def initialize(data)
        @data=data
    end

    def raise_error(data)
        raise "Attempt to create #{self.class} with #{data.class} object"

    end

    def toString()
        raise "Abstract method toString() not implemented #{self}"
    end
end

class IntItem <TreeItem
    def initialize(data)
        if data.kind_of? Integer
            super(data)
        else
            raise_error(data)
        end

    end

end



class StringItem < TreeItem
    def initilize(data)
        if data.kind_of? String
            super(data)
        else
            raise_error(data)
        end
end

Answer 1

You can write abstract method (I named it data_class) for this:

class TreeItem
  def initialize(data)
    if data.kind_of? data_class
      @data = data
    else
      raise_error(data)            
    end
  end
# ...
end

class IntItem <TreeItem
  def data_class; Integer end
end

class StringItem < TreeItem
  def data_class; String end
end

With this implementation if you will attempt to create TreeItem instance, you will get method undefined error (you can also implement custom data_class in the TreeItem to raise more specific exception).